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Bletchley Park to rebuild pioneering EDSAC computer

Will omit deadly 1940s mercury-based memory

Bletchley Park is to rebuild one of the world's first modern computers.

The Electronic Delay Storage Automatic Calculator (EDSAC) was put together at Cambridge University in the late 1940s as a tool for researchers and scientists. The room-sized valve-based system, designed and developed by the late Sir Maurice Wilkes, first ran in 1949 and served academics faithfully for nine years until its decommission in 1958.

The National Museum of Computing at Bletchley is honouring the memory of the pioneering computer with a rebuild project, expected to last around three years. Visitors to the museum will be able to see the painstaking work in progress.

The UK's Computer Conservation Society (CCS) commissioned the rebuild and has put together a budget of £250,000 to finance the project. Computing entrepreneur Hermann Hauser led the consortium that coordinated the fundraising effort.

Early phases of the project will involve going through archives and interviewing engineers who worked on EDSAC to get a better idea of how the machine functioned. The project is complicated by the fact that few parts of the original valve-based calculating machine remain intact.

"We're building up a good picture of what it was like," said Dr David Hartley, chairman of the CCS, told the BBC. "But there comes a point at which we have to guess what was in the designer's mind at the time."

Modern health and safety regulations mean that one component of the original machine, 1.5m long tubes of mercury used as a memory store, cannot be used. Scientists plan to carry out experiments to determine a suitable "delay line" memory replacement.

This workaround aside, the computer scientists are going out of their way to remain as faithful as possible to the original design.

The original had over 3000 electronic tubes used for logic, data input via paper tape and output on a teleprinter, as well as the now safety-violating mercury-filled tubes for memory, a statement on the project by the National Museum of Computing explains.

Professor Andrew Hopper, head of the computer laboratory at Cambridge University, explained: "EDSAC set computing standards for academia and commerce. It was so successful that in the nine years following 1949 it was used by Cambridge University researchers in studies such as genetics, meteorology and X-ray crystallography and even helped two researchers win Nobel prizes.

"EDSAC also led directly to the first commercially applied computer, the LEO, that broke new ground by enabling the catering company J Lyons & Co Ltd to perform payroll calculations in 1953."

The EDSAC rebuild project follows the successful rebuild of the Manchester Mark I and Colossus computers. ®

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